1. Field of the Invention
The invention relates to a semiconductor device, and more particularly, to a semiconductor device for electrostatic discharge (hereinafter abbreviated as ESD) protection.
2. Description of the Prior Art
Chips and/or Integrated circuits (ICs) are the most essential hardware foundation of the modern information society. As products based on ICs become more delicate, they also become more vulnerable to the impacts of the external environment. For example, it is found that ESD is a constant threat to modern electronics. The result of ESD on unprotected ICs is often destruction, characterized by melting or explosion of a part of the ICs. Therefore, the ESD protection devices are taken as important components of the protection circuitry provided in today's electronic devices.
Various approaches have been made to provide an ESD protection device associated with IC interface pads to prevent a core circuit of the ICs from the ESD damages. Typically, during a normal IC operation, the ESD protection device is turned off. However when an ESD event occurs, the ESD surges will cause the ESD protection device breakdown and create a substrate current path, through which the ESD current is diverted to ground and thus the core circuit is protected. The maximum withstanding voltage is the most important concern of high voltage device such as the ESD device. As the dimensional size of the semiconductor device is becoming smaller and smaller, it is getting more and more difficult to improve the maximum withstanding voltage. Furthermore, there is another problem for the ESD protection device that is the leakage may occur between the gate and the source/drain.
In view of the above, there exists a need for an ESD protection device having improved withstanding voltage and reduced current leakage.